There is a market need for a reversible key for horizontal keyway cylinder locks. A reversible key is bitted on both sides of the key blade and is thus easier to align and insert into the keyway, as it works either way it is inserted. A further use for a key that is bitted on both sides of the key blade is to operate two different cylinder locks. For example, a key blade can be bitted on one side to operate a vestibule cylinder lock when the key is inserted one way and can be differently bitted on the opposite side to operate an apartment door cylinder lock when the key is inserted the other way.
To implement a reversible key it is necessary to design a cylinder lock in which the tumbler pins that are engaged by the bitting on the side of the key blade do not seat on more than half of the width of the blade, and the bitting area on the blade must occupy no more than one-half of the width of the side of the blade. In addition, there must be sufficient strength in the center of the blade to keep the blade from breaking under the stress of applying torque to the cylinder lock. Retaining sufficient strength can be challenging if both sides of the key blade are bitted to operate a lock, as bitting the opposed sides of the lock results in a significant removal of material from the thickness of the key blade. The keys of existing horizontal cam locks have bittings that extend across almost the full width of the key blade, often leaving the key blade too weak for some applications.
Additionally, a cylinder keyway with a ward projection into the center of the bitting area of the key blade has never been employed in a cylinder having a rotating tumbler pin—sidebar cylinder. That is, there is no warding on the key blade or keyway in the portion of the key blade at which the bitting is formed. The tip of each rotating tumbler pin seats on the bitting surfaces remaining to the sides of this center ward.